Biggest issue for me is not being able to import passwords from Chrome. I have to switch back to Chrome if I need to access some web services quickly, so building up saved passwords in a browser makes it more sticky. There's probably a reason for not being able to do this though.
It also starts to get a bit sluggish when you have a couple (6-7) heavy JS/DOM tabs open.
File download UI could be better. Skip the confirmation dialog, show file and progress at the bottom of the browser window.